The present invention relates to a method of adjustment of the parameters of exposure in digital radiology, and in particular in digital mammography.
Conventionally, in radiology, the parameters of exposure such as focal track selected (in the case of a device with double focal track), filter used, voltage applied to the tube (kV), presence or absence of grid, enlargement of contact and product of anodic current by duration of exposure (mA.s), constituting what is called the configuration, are initially determined from a selection of the user for the parameters of presence or absence of grid and enlargement or contact, and from a table of automatic optimization of parameters (AOP), as a function of the selections of the user, for the parameters kV, focal track, filter and mA.s. The organ part examined is then subjected to a preexposure with a low mA.s value to determine the characteristics of the organ part examined, in particular the equivalent radiologic thickness, and the parameters of exposure are then adjusted from these characteristics.
More precisely, at the time of preexposure an automatic exposure control (AEC) cell is used and the equivalent radiologic thickness is determined from the signal of the AEC cell. In order to obtain a good estimate of the equivalent radiologic thickness, 60 different parameters must be determined by means of the AEC calibration cell. An estimate of the composition of the organ part examined and an adjustment of the parameters of exposure (configuration) is then made with an initial estimate of mA.s.
During an exposure of the organ part examined with the previously determined configuration, the AEC cell continuously updates the mA.s value.
For further details concerning the method described above, reference is made to documents EP-0,402,244 and EP-0,465,360.
The method of adjustment of the configuration described above has the disadvantage of necessitating a specific calibration device, namely the AEC cell, and of requiring the determination of a large number of parameters.